Virtually anyone responsible for maintaining a lawn or the like is familiar with thatch, that brown layer of dead grass and vegetation which covers the ground surface. Aside from its unattractive appearance, thatch can cause problems in a lawn. Excess thatch can encourage grass root development above the surface of the soil (within the thatch) promoting "brown-off" and winter injury; and it may increase watering needs to maintain greenness. Thatch can make mowing more difficult when the "spongy" surface allows the mower wheels to sink down into the lawn. Thatch provides a home for insects and lawn disease. Thatch can restrict water and air movement into the soil. In addition, thatch can affect the downward movement of pesticides and fertilizers into the soil.
Many devices have been developed in an effort to remove thatch from a ground surface. One of the most common methods of thatch removal is a hand-held rake. The rake tines are drawn across the ground surface dislodging thatch and plant matter. This method of removing thatch suffers many drawbacks. Raking can be unpleasant, strenuous and time consuming. Raking can cause injuries to the back and hands of the worker. In addition, the thatch must be collected and removed to a compost pile or put in an appropriate waste receptacle.
Several variations on the rake have been developed in an effort to better remove thatch. One such device is a motorized dethatcher designed to be towed behind a tractor. This device has a single rotatable shaft with a plurality tines projecting radially from such shaft. The shaft is rotated by a motor. The rotating tines contact the ground surface and remove thatch. This device is expensive and costs approximately twice the price of the present invention. Another drawback is that the device does not deposit the thatch in a collector bag and simply redeposits the thatch on the ground surface. Thus, additional time and effort must be expended to collect and dispose of the thatch.
Other dethatchers include tines which do not rotate and are mounted in front of or behind a tractor. In each of these devices, a plurality of tines project downward toward the ground from a horizontal surface secured to the tractor. As the tractor moves, the tines are drawn across the ground surface to loosen thatch. All of these designs are less than satisfactory because tine tip speed is limited to the speed of the tractor. This means that dethatching is often incomplete requiring additional work. Another drawback is that the tines are perpendicular to the ground rather than swept back at an angle and, therefore, tend to break and dig into the ground causing damage to the ground surface. These prior art dethatchers do not collect the thatch which they remove. Accordingly an expensive sweeper attachment for the tractor is required or additional time consuming efforts must be taken to collect and remove the lawn debris.
Yet another type of prior art dethatcher is a ground-device and manually pushed by the operator made by Noma Outdoor Products, Inc. This device utilizes a single rotatable tine shaft with a plurality of tines projecting radially therefrom. The ground-driven tine shaft rotates in response to forward motion of the device.
Such ground-driven dethatching devices have a number of disadvantages. The device is heavy and difficult to push. Another disadvantage is that torque provided by a drive wheel is often inadequate to rotate the tine shaft. Due to loading and terrain conditions, torque to rotate the tine shaft is often supplied primarily by one drive wheel. Such torque is frequently insufficient to overcome resistance to tine shaft rotation (for example, when the dethatcher encounters an obstruction) causing the tine shaft and drive wheel to stop rotating and the wheel to skid. Another drawback is that tine tip speed is limited by the rate at which a human can push the device.
All of the prior art dethatchers, with the exception of a hand-held rake, have a further disadvantage in that the tine height is not automatically adjusted in response to loading conditions, irregular terrain or striking an obstruction such as a rock. Without apparatus to automatically raise the tine height, resistance to tine shaft rotation may become excessive causing the tine shaft and drive wheels to stop rotating or cause the tines to break.
Clearly, an inexpensive lawn dethatcher with a tine shaft drive linkage which supplies adequate torque to rotate the tines, automatically adjusts tine height to terrain conditions and collects the thatch which it removes would be a significant improvement.